The current invention relates to an apparatus and method for measuring the angular position of a rotatable body, in particular a body which can rotate by more than 360xc2x0, according to the preambles to claims 1 and 3.
In various devices, in particular in devices which are intended to aid in the detection of the angular position of a rotatable shaft, it is necessary to know the precise position of the shaft immediately before initiating operation of the device. This requirement can best be achieved with the aid of analog angle sensors, for example potentiometers, which, after being switched on, immediately output the effective angular position value in each position, in the form of a voltage.
If such devices are used for angular measurement of angular ranges that are greater than 360xc2x0, the problem arises that it is no longer possible to determine which rotation the shaft is currently in. In order to evaluate angular ranges that are greater than 360xc2x0, though, incremental position transducers can be used in which the angular position is detected by forward and backward counting of pulses. However, incremental position transducers of this kind cannot be used to execute absolute angle measurement because only those increments which move past a pickup can be counted.
DE-OS 195 06 938 has disclosed an apparatus for detecting the angular position of a rotatable body which has a number of uniform angle markings or teeth and has at least two additional rotatable bodies which have a different number of uniform angle markings or teeth. In this connection, the rotation angle of the two additional rotatable bodies is detected and based on these, the angular position of the rotatable body is determined. The rotating bodies used in this case are gears, wherein the rotatable body to be measured has n teeth and the two additional gears have m and m+1 teeth.
The object of the invention is to produce an apparatus and a method with which it is particularly simple to measure an angle of a rotatable body, in particular a body which can rotate by more than 360xc2x0.
This object is obtained by means of an apparatus with the characteristics of claim 1 and a method with the characteristics of claim 3.
According to the invention, it is possible to detect the angular position of a rotatable body, for example a steering wheel, in a very simple and error-tolerant manner. Particularly when using a greater number of additional rotatable bodies which cooperate with the rotatable body, a higher degree of error tolerance and a better angular resolution is produced in comparison to conventionally known systems.
The angles xcex8 and "psgr" of the additional rotatable bodies can be suitably detected by means of periodic angle sensors and the angle xcex1 Of the first rotatable body can be suitably determined in an evaluation circuit by taking into account the angles xcex8, "psgr" and the numbers n, ni, nj of the respective angle markings. If periodic angle sensors of this kind are used, it is very simple to mathematically evaluate the angles xcex8 and "psgr" by taking into account the respective numbers of angle markings since the evaluation can be executed by means of trigonometric functions.
According to a preferred embodiment of the apparatus according to the invention, the angle sensors operate in pairs as absolute value transducers and in particular are embodied as AMR angle sensors, which scan magnets which are connected to the additional rotatable bodies. AMR angle sensors of this kind are relatively inexpensive to obtain and prove to be very rugged and reliable in actual use.